Corrosion occurs on metals and results in corrosion products. Measurements of the degree and amounts of localized and general corrosion have typically been made by visual inspection with an inspector often relying on his or her experience and on reference cards containing images of surfaces that are corroded to varying degrees. Visual corrosion inspections thus involve a degree of subjectivity.
Corrosion inspection is important for monitoring in-service equipment, structures, and vehicles. Inspection is also important for manufacturing quality control and evaluating the performance of anti-corrosion coatings. In manufacturing quality control, monitoring of the application of anti-corrosion coatings to metal surfaces often is done by periodically coating test coupons of a metal substrate, exposing the coated test coupons to a corrosive environment, and then visually inspecting the test coupons for localized or general corrosion products.
Similarly, in evaluating new corrosion coatings, test coupons are coated with different formulations of the corrosion coatings. These test coupons are exposed to a corrosive environment, and then visually inspected for corrosion products. Such a visual inspection of the test coupons for quality control and for grading coatings after exposure to a corrosive environment involves a degree of subjective judgment by the visual inspector.
Corrosion inspection monitoring, anti-corrosion coating application, and the evaluation of new corrosion coatings are important for many types of equipment, structures, and vehicles exposed to corrosive environments or weathering. By way of example, corrosion control for aircraft constructed with aluminum alloys is important due to the range of environments to which aircraft are exposed to, and the lifetime over which the aircraft are exposed those environments. Currently, corrosion inspection, manufacturing quality control of corrosion coatings application, and evaluation of new corrosion control coatings for aluminum alloys, for aircraft, is performed visually as described above.
Therefore, there exists an unmet need in the art for a non-destructive quantitative means of determining the degree and amounts of localized or general corrosion on metallic substrates.